The 73-year-old musician has revealed he completely forgot numerous tracks he thought up with his bandmate John Lennon in the 1960s because they had no method of recording the melodies and would forget them by the time they reached the studio.

He explained: ''Things have changed quite a bit.

''You've got recording devices now which change the songwriting process. For instance, John and I didn't have them when we first started writing, we would write a song and just have to remember it.

''And there was always the risk that we'd just forget it. If the next morning you couldn't remember it - it was gone. In actual fact you had to write songs that were memorable, because you had to remember them or they were lost! There must have been dozens lost this way.''

The rocker - who has most recently been working with rapper Kanye West - continued to say he has ''millions'' of songs ready to be recorded nowadays because the advancement in technology allows him to make a note of his ideas.

He told the Evening Standard newspaper: ''We didn't have tape recorders. Now you can do it on your phone. So you would have to form the thing, have it all finished, remember it all, go in pretty quickly and record it. Now, because you can get things down on a device, I've got millions of things I want to record and do.''